1. Field of the Invention
The present invention generally relates to filter devices, and more particularly to a tunable filter device.
2. Description of Prior Art
Bragg gratings are well known and widely used in a variety of optical applications. In general, a Bragg grating is formed by providing a periodic variation in the refractive index of the core of an optical fiber or a planar waveguide. The periodic variations of gratings cause reflection of a particular Bragg wavelength. All other incident wavelengths are transmitted through the grating.
However, a conventional filter device using the Bragg grating has a shortcoming. That is, the wavelength of the reflected light is fixed when the filter device is manufactured.
Therefore, a filter device which can be tunable to reflect a wavelength within a range of different wavelengths is desired to overcome the shortcoming of the prior art.
Accordingly, an object of the present invention is to provide a tunable filter device.
To achieve the above-mentioned object, a tunable filter device in accordance with the present invention includes a plurality of input waveguide channels, a plurality of output waveguide channels and a Bragg grating which are formed in a planar waveguide. Every input waveguide channel couples with the Bragg grating at a different angle, and every output waveguide channel is a mirror image of a corresponding input waveguide channel. When input light is transmitted through a particular input waveguide channel, light of a particular wavelength is reflected by the Bragg grating into a corresponding, mirror image output waveguide channel.